(1) Field of the Invention
The present invention relates to a fluid dynamic bearing apparatus which supports a shaft member in a non-contact manner by the hydrodynamic effect of a fluid which is produced in a bearing gap.
(2) Description of the Related Art
This fluid dynamic bearing apparatus is for use in spindle motors for disk apparatuses, polygon scanner motors for laser beam printers (LBP) and in other small motors. Enhanced speed, cost reduction, noise reduction, etc., as well as high rotational accuracy, are required for these motors. One of the components which determine these required performances is a bearing which supports spindles of the motors. In recent years, the use of a fluid dynamic bearing having excellent characteristics for the above required performance has been considered or actually used. For example, in a spindle motor of a disk drive unit such as HDD, a fluid dynamic bearing apparatus which uses a fluid dynamic bearing for each of a radial bearing portion which supports a shaft member in the radial direction and a thrust bearing portion which supports the shaft member in the thrust direction is used. In this fluid dynamic bearing apparatus, hydrodynamic grooves are provided as a hydrodynamic pressure producing means on the inner circumferential surface of a bearing sleeve which forms the radial bearing portion or on the outer circumferential surface of the shaft member. The hydrodynamic grooves are also provided on both end faces of a flange portion of the shaft member which forms the thrust bearing portion or on the faces opposing these (end faces of the bearing sleeve, end faces of a thrust plate, etc.) (for example, refer to Japanese Unexamined Patent Publication No. 2003-239951).
When these hydrodynamic grooves are formed, especially when the hydrodynamic grooves are formed on the inner periphery of the bearing sleeve, the method of processing the hydrodynamic grooves is critical. As an examples of such a processing method, a method comprising inserting a mold having a groove pattern corresponding to the shape of the hydrodynamic grooves at the inner periphery of a bearing sleeve material, and then pressing the bearing sleeve material in the radial direction in a state of being bound in its axial direction to thrust its inner circumferential surface against the mold and cause plastic deformation is suggested (for example, refer to Japanese Unexamined Patent Publication No. 11-190344).